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Transcript
W5D3H3: Sensory Receptors Learning Objectives 1. Outline properties of sensory receptors including how intensity (strength) and duration are encoded and adaptation to stimulus. 2. Discuss the importance of the frequency of action potentials and its relationship to neurotransmitter release and stimulus coding. 3. Give examples of how sensory receptor properties are utilized by cutaneous receptors to detect and encode input. 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells). Why This Topic? • Understanding how external signals are detected and encoded by the nervous system is essential to a bigpicture understanding of how stimuli are detected and interpreted by the nervous system. Because defects in this process constrain the well-being and quality of life for many people and because changes in how stimuli are detected and integrated can be used to identify more serious conditions, it is essential to understand this process. This material also integrates physiology, HFF, and clinical topics by explaining how nerve damage from diabetes can alter neuronal signaling. LO 1. Outline properties of sensory receptors including how intensity (strength) and duration are encoded and adaptation to stimulus Primary problem: How do we get information about the outside world and the inside world? Labeled lines: sensory nerve cells carry information to the spinal cord and brain about specific types of stimuli. Abstract In the somatosensory system, various different sensory receptors capture different stimuli and convey them to the sensory cortex. Each type of receptor is specialised, that is, receives the stimulus to which it is predetermined to receive. Immediately as it is stimulated, the receptor sends a signal to the somatosensory cortex, via nerve fibres, and the area of the cortex that receives the signal determines the mode of the consequent perception. This mechanism is called principle of the "labelled" lines. The somatic receptors are the structures designated to receive stimuli, however, if their afferent fibres are stimulated at any point when approaching the cortex, the mode of perception by the cortex is the same as when the somatic receptor is stimulated directly. This occurs after the amputation of a limb, wherein the remaining fibres transmit to the cortex the mode of sensation for which they were specialised, despite the lack of somatic receptors at the beginning of the afferent pathway. However, the afferent pathway ends at the same cortex area as before the deafferentation. Since the somatic receptors and the integrity of afferent pathways are important to the regulation and modulation of the received stimuli, after the deafferentation the afferent pathway becomes anatomically and functionally abnormal. We believe these factors, involved in the pathophysiology of phantom limb (PHL), might be the explanation for this intriguing phenomenon. Somatosensory Homunculus Figure 10-9 LO 1. Outline properties of sensory receptors including how intensity (strength) and duration are encoded and adaptation to stimulus Three classes of sensory receptors: (a) free nerve endings, (b) with accessory structures, and (c) specialized receptor cells. LO 1 & LO 2. Outline properties of sensory receptors including how intensity (strength) and duration are encoded and adaptation to stimulus. Discuss the importance of the frequency of action potentials and its relationship to neurotransmitter release and stimulus coding. Transmitter release More transmitter release LO 1 . Outline properties of sensory receptors including how intensity (strength) and duration are encoded and adaptation to stimulus. LO 3. Give examples of how sensory receptor properties are utilized by cutaneous (skin) receptors to detect and encode input. Area on the skin that receptor responds to rapidly adapting slowly adapting rapidly adapting slowly adapting LO 3. Give examples of how sensory receptor properties are utilized by cutaneous (skin) receptors to detect and encode input. Area on the skin that receptor responds to rapidly adapting Fine touch < 50 Hz slowly adapting rapidly adapting Light pressure Vibration > 50 Hz slowly adapting Stretch LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells). LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells). LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells). LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells). LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells). LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells). LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells). depolarization LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells). Taste buds. Each taste bud is composed of taste cells joined near the apical surface with tight junctions. Taste ligands create Ca2 signals that release serotonin or ATP. Sweet Umami Bitter Sour (CO2) Tight junction Type I support cells Taste buds are located on the dorsal surface of the tongue. may sense salt when Na enters through Na channels. Taste pore Salt? Presynaptic cell (III) (Adapted from Tomchik et al., J Neurosci 27(40): 10840–10848, 2007.) ATP Serotonin Receptor cells (type II) Light micrograph of a taste bud Primary sensory neurons LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells). Panx1 LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells). HPHY 241 26 Figure 10-16c LO 4. Compare and contrast sensory receptor physiology (photoreceptors, olfactory receptors, gustatory receptors and hair cells). END Somatosensory Cortex 4. 5. It is in the somatosensory cortex that the brain recognizes where the ascending sensory tracts originated i. Each sensory tract has a corresponding region on the cortex Within each region, columns of neurons are devoted to particular types of receptors Fig. 9.10 HPHY 241 33 HPHY 241 34 HPHY 241 35 HPHY 241 36 HPHY 241 37 4. The tectoral membrane and hair cells HPHY 241 38 HPHY 241 40 HPHY 241 41 HPHY 241 42 HPHY 241 43 HPHY 241 44 HPHY 241 45 HPHY 241 46 HPHY 241 47